Recently, development of a new technique for minimizing a leakage current due to wet installation has emerged as research and development of a heating material for energy-saving heating and a heater using the heating material are accelerated.
A wire heater has mainly been used to date as a wet installation type heater for heating. However, since the wire heater is prepared from a heating material such as Ni—Cr and Fe—Ni—Cr, thermal efficiency is low due to line heating. Thus, power consumption is relatively high and there are difficulties in maintenance, for example, the entire heater doesn't heat when a circuit is opened at any point due to a series circuit configuration. Also, due to an overheating phenomenon, such as local heating, e.g., heat collection, the damage to the heater and the risk of fire are high and the safety of the product is not provided.
Furthermore, a carbon-based plane heater has better thermal efficiency than the wire heater, but since conductive particles, such as carbon black, are used as a resistance heat source, a resistance value is significantly changed due to repeated use and, due to the overheating phenomenon, such as local heating, e.g., heat collection, the damage to the heater and the risk of fire are high and the safety of the product is not provided.
In order to secure the safety, a temperature control system, such as an overheat protection sensor, has been provided to the wire heater and plane heater, but the temperature control system causes the overheating phenomenon, such as local heating, e.g., heat collection. The overheating phenomenon mainly occurs from thermal insulation or heat accumulation and overheating, and particularly, since local overheating of the heater damages a finishing material while the temperature of a heat accumulator is rapidly increased, it has been a cause of electrical fires.
In particular, in a case in which limitations of the wire heater, which has currently been installed for wet use, are addressed and the plane heater having relatively better thermal efficiency is used as a heater for wet installation, since the leakage current is more rapidly increased than that of the wire heater, a circuit breaker may be operated.
The reason for this is that a conventional plane heater has mostly been prepared from a polyethylene terephthalate (PET) film for the purpose of electrical insulation and flame retardant and has mainly been used in dry installation. Also, there is a limitation in that the
PET film of the plane heater is vulnerable to strong alkalinity of a cement mortar floor in contact therewith during wet installation and to the generation of moisture or condensation due to waterproofing properties caused by interfacial contact in which the PET film of the plane heater has a wider installation floor surface than the wire heater.
A constant heater using a positive temperature coefficient (PTC) constant heater-ink polymer, in which a PET film is used, has been proposed in Korean Patent No. 10-1168906 (Jul. 7, 2012) by the present applicants, the patent gazette discloses solutions to problems, for example, an improvement in polymer PTC characteristics and the stabilization of room-temperature resistance by the adjustment of the amounts of various dopants added, and the patent has already been commercialized and products have exported to the United States.
However, with respect to the patented technique, the polymer PTC constant heater saves energy and is safe from the risk of electrical fires due to self-temperature control characteristics, but there are difficulties in using the heater for wet installation as described above.
Thus, the present invention uses and improves the patented technique developed by the present applicants to propose a completely new wet-use plane heater having self-temperature control characteristics which may minimize a leakage current and may be wet-installed for heating.